BAGHDAD
— A massive funeral tent stood on the street in Baghdad's Al Amel neighborhood. Taped verses from the Koran echoed from loudspeakers. Black-clad women wailed and slapped their faces in sorrow.

On the surface, the scene last week was nothing unusual for Baghdad. But instead of mourning those killed by insurgents or militiamen, this time residents grieved for a mother and two of her adult sons killed in a US helicopter strike earlier this month.

While the Americans insist those killed were insurgents who had previously fired "small arms" with "hostile intent" on a US combat outpost (COP), neighbors see it differently. Witnesses say the men weren't firing on Americans, but reacting to what they thought was a Sunni insurgent attack. It proved to be a deadly mistake in the ever more dense fog of war in Iraq.

Residential alleyways and streets are now becoming battlefields. Infantrymen, trained mainly to engage and kill the enemy and protect themselves from attacks, are being asked to tackle a sectarian war in which the battlefields are neighborhoods and the enemy is becoming harder to spot.

"The problem with the Army is that they are here to fight and it's all about combat power when it's no longer that kind of a war," says a US military officer stationed in Iraq and who is critical of many aspects of the Baghdad security plan.

There is no question that the number of Iraqi civilians killed at the hands of US troops is a mere fraction of those falling every day to car bomb and suicide attacks. But when Iraqis do get caught in American crossfire for whatever reason, those deaths, and the often confusing aftermath of investigations and the paperwork for compensation, only serve to fuel the anger and animosity of Iraqis toward US troops.

Four years into the war, human rights groups complain there is a lack of transparency and adequate compensation by the US military to the families of victims in incidents such as the one in Amel.

"The data is so tightly held [by the US military] that we have a hard time wrapping our heads around the extent of the problem," says Marc Garlasco, senior military analyst at New York-based Human Rights Watch.

And, experts say, the lack of information about incidents in which civilians are killed is preventing the Army from learning from its mistakes, and preventing such incidents in the future. "The information is not making it into lessons learned," says Mr. Garlasco.

Earlier this month, US government documents released by court order to the American Civil Liberties Union showed that only one-third of the families of 479 Iraqi civilians killed by US soldiers between 2003 and 2006 received compensation after filing for claims, while very few incidents were forwarded for further investigation.

The incident in Amel may be a case study in the confusion that rules throughout Baghdad. Khalid Abdel-Jawad, a civil engineer who is a fluent-English speaker, says he's still finding it hard to understand why the US military killed two of his best friends and their mother and continues to hold his wounded teenage brother.

It all started sometime before midnight on Sunday, April 15, when many residents of Amel's 803 block were roused from bed by the sound of gunfire and explosions.

"We all thought it was the Janabat at it again," said Mr. Abdel-Jawad, referring to members of the Janabi tribe to which most of Amel's Sunni Arab residents belong.

Like many neighborhoods in Baghdad, Amel is now clearly segregated along sectarian lines. In this case the fault line is the 130-foot-wide wide Seven Nisan (April) street, the area's main shopping street. Many of the entrances to alleyways on both sides are blocked by concrete barriers and concertina wire, providing physical barriers in a city where the US has already started to build a wall to protect a Sunni enclave. On Monday, Prime Minister Nouri al-Maliki ordered a stop to the construction.

In Amel, the running joke among Abdel-Jawad and his friends is that they, the Shiites, live in North Korea while the Sunnis live in Janabi Korea, a pun on the Arabic word for south, which is janoub.

That night, a spokesman for the US military said that soldiers from the 1st Battalion, 28th Infantry Regiment stationed on the Sunni side of the neighborhood came under attack at the same time indicated by Abdel-Jawad.

After hearing the gunshots and explosions, Abdel-Jawad said that his brother Ahmed, 17, grabbed his AK-47 and rushed out of the house. Many of the neighborhood's male residents had done that in the past when they thought they were being attacked by Sunni militants.

"In a situation like this we must be alert and ready to defend ourselves. It's difficult to rely on the Americans and the Iraqi Army to protect us," Abdel-Jawad said.

Young Ahmed was joined by his neighbor and a friend, Abbas Abdel-Khodr, according to witnesses. Moments later Mr. Abdel-Khoder's mother, Souad, and her other son, Ali, tried to persuade them to come back in, according to Abdel-Jawad.

Meanwhile, US soldiers at the outpost called for helicopters into the area to confront the source of gunfire.

Ahmed and Abdel-Khodr went to the top of an alleyway and fired shots in the air, apparently thinking they might scare away the perceived Sunni attackers.

"Four anticoalition forces were positively identified by attack aviation," said Maj. Kirk Luedeke, spokesman for the 4th Brigade, 1st Infantry Division to which the 1-28 is attached. "The helicopters returned fire at the individuals engaging our troops, killing them after clearly establishing hostile intent."

When the sound of explosions and gunfire quieted, Abdel-Jawad ran out of his home to look for his brother and friends. "It was like huge firecrackers. The earth shook. I went out and saw Ali's body and just the remains of his mother. I was sick. I could not take it. I went back home."

Later, Abdel-Jawad and other residents of Amel said US and Iraqi forces came into the area and picked up the three bodies and Ahmed, who was badly wounded.

The next morning, Abdel-Jawad went to an Iraqi Army outpost in the area manned by a Kurdish unit to inquire about the fate of his brother. "The first thing they asked me was whether I was Sunni or Shiite. I was shocked," said Abdel-Jawad.

"When I told them Shiite, they said 'check with the Americans.' When I kept insisting, they said 'Leave or we will arrest you.' "

Abdel-Jawad and his family were only able to find out one week later from the US military that Ahmed was still alive and that he was being held now at a maximum-security detention facility in Baghdad.